1. Field of the Invention
The present invention relates to a ball screw structure, and more particularly to a preload structure for a ball screw located inside a nut, which can be utilized to achieve the preload objective to reduce the number of the circulation system fittings, shorten the length of the nut, reduce the extra machining and achieve various preload changes by controlling the deviation of the interval helical track during rubbing.
2. Description of the Prior Art
The linear drive technology and its products have been the most important portions of many precision machine tools for the constant research and the improvement on the precision feed system. Various linear products have come into our everyday life, manufacturing factories and high-tech equipments. Although the technology of the ball screw is developing quite fast, consumers still expect optimum to come. Therefore, improvement has to be made. Such a desire for constant improvement of technology is quite strong in many high precision mechanism-manufacturing fields (such as wafer process equipment, CNC equipment, etc) that require more stability and less noise). For this matter, the existing linear mechanism needs a better solution.
Generally, the ball screw used on the market must be designed with a structure inside, which produces bias pressure to support every element therein stably. As shown in FIG. 1, a conventional ball screw structure disclosed by US Patent No. 2005/0000309 comprises a screw (not shown), a nut 10, a plurality of rolling elements 11 and two circulation systems 12, 13. The outer surface of the screw is formed with a helical groove. The inner surface of the nut 10 is formed with a helical groove 101. The two circulation systems 12, 13 are disposed on the front end and the back end of the nut 10 respectively, so as to make rolling elements 11 which have passed through the helical groove 101 circulate at the front end and the back end of the nut 10.
The abovementioned ball screw structure uses a single nut 10 to offer bias preload function. Generally, a void tooth 102 between the two unattached circulation systems 12, 13 produces a lead deviation to make the rolling elements 11 in the two independent circulation systems 12, 13 bear outwards-drawing symmetric forces. Since the preload is a necessary design and the conventional nut 10 must be installed with two circulation systems 12, 13, the machining of each circulation device 121, 131 and each section of circular path causes the conventional ball screw to produce the following technology bottlenecks:
First, the number of the fittings of the conventional ball screw is large and the number of the machining procedure is large, the inner design is complicated and difficult to machine, so the cost of the conventional ball screw is high.
Second, the conventional ball screw utilizes a void tooth 102 between the two independent circulation systems 12, 13 to do the lead deviation, but the existence of the void tooth causes the length of the nut to be increased, thus causing limitations in design and waste.
Third, the two independent circulation systems 12, 13 must be installed with four built-in circulating devices 121, 131 in total, thus increasing the machining difficulty.
It is known from the abovementioned products, the problems caused by the conventional preload design are the emphasis that the producers expect to improve. If the producers want to change the preload direction, the designs of the circulation systems, void tooth, the lead and the nut must be completely changed.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.